A moth is an insect closely related to the butterfly. Both are of the order Lepidoptera. People who study or collect these insects are called lepidopterists. Most species of moths are nocturnal, but there are crepuscular and day-flying species.

Moths are commonly regarded as pests because the larvae of a few species eat fabric such as clothes and blankets. These can be repelled by the scent of wood from juniper and cedar, or naphthalene (the chemical used in mothballs).

Moths are notable for apparently being attracted to light, or more specifically, are known to circle ambient objects. The reason for this behaviour is not known. Moths do not fly directly away from the light due to a visual distortion called a Mach band. One researcher, Henry Hsiao, has conjectured that moths, as nocturnal creatures, fly towards the darkest part of the sky in pursuit of safety. Moths are thus inclined to circle ambient objects in the Mach band region, usually at a radius of about one foot, depending on the species.

Night blooming flowers usually depend on moths (or bats) for pollination, and artificial lighting can draw moths away from the flowers, impacting the plant's ability to reproduce. Light pollution is coming under increasing scrutiny as a source of many subtle ecological changes.

Moths of the type understood to be "attracted to light" are, instead, flummoxed by the proliferation of artifical lights in their local environment, which, if brighter than the brightest celestial object (e.g., the moon), will usurp that object's significance as the reference point for the moth's flight. To travel in a straight line, a moth would maintain the same angular relationship with the (relatively stationary) moon. Encountering a brighter artificial light, as the moth maintains its angular relationship to the source of light (per its evolved mode of navigating), but, because the light is nearby, that consistent angle results in a decreasing spiral, until the moth strikes the light source.